<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>缓存全局变量</title>
    <style>
      #id {
        color: #fff;
      }
    </style>
  </head>
  <body>
    <input type="button" value="btn" id="btn1">
    <input type="button" value="btn" id="btn2">
    <input type="button" value="btn" id="btn3">
    <input type="button" value="btn" id="btn4">
    <p>111</p>
    <input type="button" value="btn" id="btn5">
    <input type="button" value="btn" id="btn6">
    <p>222</p>
    <input type="button" value="btn" id="btn7">
    <input type="button" value="btn" id="btn8">
    <p>333</p>
    <input type="button" value="btn" id="btn9">
    <input type="button" value="btn" id="btn10">

    <script>
      function getBtn() {
        let oBtn1 = document.getElementById('btn1')
        let oBtn3 = document.getElementById('btn3')
        let oBtn5 = document.getElementById('btn5')
        let oBtn7 = document.getElementById('btn7')
        let oBtn9 = document.getElementById('btn9')
      }

      function getBtn2() {
        let obj = document // 缓存全局变量
        let oBtn1 = obj.getElementById('btn1')
        let oBtn3 = obj.getElementById('btn3')
        let oBtn5 = obj.getElementById('btn5')
        let oBtn7 = obj.getElementById('btn7')
        let oBtn9 = obj.getElementById('btn9')
      }

    </script>
  </body>
</html>
